The methods of the embodiments described herein relate to acid diversion treatments in injection wells using permeability modifiers.
An injection well is a wellbore in subterranean formation used to pump fluids into a producing reservoir (e.g., a hydrocarbon producing reservoir). Injection wells are typically used for waterflood, pressure maintenance, and enhanced oil recovery purposes. Injection wells are often composed of multiple subterranean zonal portions that are not homogeneous in terms of permeability, porosity, and/or the degree of damage experienced in the particular zone compared to surrounding zones. These nonhomogeneous zones can impede fluid injectivity into producing wellbores and may require increased pressure to adequately inject fluids.
It is common to perform acid diversion treatments in injection wells to combat the nonhomogeneous nature of the well. An aqueous acid treatment may be injected into an injection well, where the acid is expected to dissolve portions of the formation rock in the near wellbore region, thereby reducing the lack of zonal homogeneity in the injection well. Acids, however, follow the path of least resistance and tend to flow to high permeability zones. In order to uniformly treat an injection well with an acid, diversion techniques are typically employed. Diversion techniques encourage the acid to flow from high permeability zones to low permeability zones.
Permeability modifiers have been effective acid diverters for hydrocarbon producing wells. They are capable of altering the relative permeability of a portion of a wellbore that they come into contact with, resulting in blockage of water production and/or diversion of aqueous fluids away from that portion of the wellbore. As such, they are particularly useful in hydrocarbon producing wells where they have no effect on hydrocarbon permeability and where there is no concern that the effects of the permeability modifier (e.g., reduction in water permeability) may remain in effect for a period longer than desired or permanently. Injection wells, on the other hand, typically involve injection of water rather than hydrocarbons and minimal pressure during fluid injection is desirable. Thus, the use of permeability modifiers, although effective acid diverters, in injection wells may result in undesirable or irreversible reduction in water permeability of the wellbore.
It is therefore desirable to provide an acid diversion treatment for use in an injection well comprising a permeability modifier, whose effects can be reversed after the treatment is complete.